Tractor four wheel drive

ABSTRACT

A four wheel drive for a vehicle having means for synchronizing the ground speeds of the front wheels and the rear wheels through selectively different drive ratios between the front and rear wheels as the front wheel rolling radius is changed.

I Unlted States Patent 1 [111 3,763,947 Longshore Oct. 9, 1973 [54]TRACTOR FOUR WHEEL DRIVE 2,775,903 1/1957 Reed 74/325 [75] Inventor:Donld w. Longshore New Berlin, 2,436,746 2/1948 Drought 74/325 Wis.

. Primary Examiner-Kenneth H. Betts 7 l 3] Asslgnee it gf gfigz s fAssistant Examiner-J. M. McCormack I AttorneyArthur L. Nelson et al.[22] Filed: Sept. 21, 1971 [21] Appl. No.: 182,376

[57] ABSTRACT [52] 1.5. CI. 180/44 R, 74/325 A four wheel drive for avehicle having means for [51] Int. Cl. B60k 17/06 chronizing the groundspeeds of the front wheels and 0f SCII'C]! R; the rear wheels gh i lydifferent drive tios between the front and rear wheels as the front [56]References cued wheel rolling radius is changed.

UNITED STATES PATENTS 2,314,833 3/1943 Keese 180/44 R 10 Claims, 5Drawing Figures PATENTEDUCT n I SHEET 1 (1F 3 PATENTEDBBT 91w 3.763.947

, snau a or 3 I 8) A A A TRACTOR FOUR WHEEL DRIVE This invention relatesto a four wheel drive vehicle and more particularly to selectivelychanging the drive ratio to the front wheels to synchronize the groundspeed of the front and rear wheels with changing of rolling radius ofthe front wheels.

The conventional rubber tired tractor drives through the rear wheels andunder most circumstances the tractive effort delivered bythe rear wheelsis adequate for the work performed. Under unusual circumstances,however, where maximum traction is necessary, it is desirable to haveadditional tractive effort available on the front wheels. Whilemechanical front wheel drive does not require additional pumps andmotors and by draulic conduits to drive the front wheels, synchronizingmeans for sychronizing the ground speed of the front and rear tires maybe necessary.

The ground speed of a wheel varies with the tire size, tread andinflation. Also with a change in tires on the front wheels or the rearwheels it becomes necessary to coordinate the ground speed for each ofthe tires. The optimum condition for ground speed of the tires is wherethe front tires are slightly faster than the ground speed of the rearwheels. Thisspeed should be between -2 percent faster than the rearwheels so the front wheels have a tendency to pull the tractor. It isunderstood that during normal operation of the tractor a certain amountof slippage is inherent while the tractor is pulling. This must also beaccounted for in determining the tire speed of the front and rearwheels. Travel reduction speed due to slippage has been recorded betweenl0 and 20 percent so that the front and rear wheels will alwayscontribute to the drawbar pull, even though they are not travelng at thesame speed, but for most ideal operations, as previously indicated, itis preferable to have the front wheels traveling slightly faster thanthe rear wheels which provide for more stability and better control ofthe tractor during operation.

Accordingly, some means must be provided to vary the speed ratio betweenthe frontand rear wheels to provide optimum ground speed between thefront wheels and the rear wheels under all conditions. Accordingly, thisinvention provides a means in the front wheel drive which willselectively vary the speed ratio to the front wheel drive and controlthe ground speed of the front wheels relative to the rear wheels toprovide optimum operating conditions and maximum traction in amechanical four wheel drive.

It is an object of this invention to provide a four wheel drive for avehicle having means for changing the drive ratios of the front wheelsrelative to the rear wheels to provide the desired tire speedrelationship on the ground surface between the front and rear wheels.

It is another object of this invention to provide a four wheel drivewith a power transmission driving to the rear wheels and a powertransfer to the front wheel having means for changing the gear ratio toaccommodate a selected change in rolling radius of the frontv wheels.

It is a further object of this invention to provide a four wheeldrive ona vehicle and more particularly for selectively changing the gear ratioto the front wheels relative to the rear wheels with change in tiresizes of the front wheels with relation to the rear wheels.

It is a further object of this invention to provide a four wheel drivein a vehicle with means for selectively 7 The transfer gearbox includesa driven gear driven by a driving gear in the transmission withthe gearsoperating on selected gear centers with means for mounting a driven gearon one of at least two gear centers. The driven gear is one of aselected number of gears each having a selected number of gear teeth toprovide different gear ratios for driving the front wheels. The toothprofiles of each of the selected gears vary slightly to accommodateoperating with different pitch diameters to thereby provide a means forchanging the gear ratio to drive the front wheels with relation to therear wheels.

The speed ratios of the front and rear wheels operate withinpredetermined limits in order to provide the desired traction and toreduce tire wear. This provides the optimum ground traversingrelationship between the front and rear wheels.

The preferred embodiments of this invention are illustrated in theattached drawings.

FIG. 1 illustrates a side elevation view of the vehicle with two wheelsremoved to more clearly show the relationship of the drive mechanism.

FIG. 2 is a cross section view taken through a portion of thetransmission and the transfer gear case.

FIG. 3 is a cross section view taken on line IIIIII of FIG. 2.

FIG. 4 is a modification of a cross section view similar to FIG. 3.

FIG. 5 is a cross section view illustrating tooth profiles of gears withthe driven gear in the transfer gear case operating with different pitchdiameters and having different numbers of teeth.

Referring to the drawings, a tractor 1 is mounted on a pair of rearwheels 2 and a pair of front wheels 3. The engine 4 mounted on thechassis 5 drives through the transmission 6 and the rear end driveassembly 7 to the rear wheels 2. The transfer gear casing 9 is mountedon the underside of transmission housing 10.

A suitable control lever 11 is pivotally mounted on the housing 10 forselectively engaging the front wheel drive. The front wheel driveincludes the drive shaft 12 driving the propeller shaft 13 which drivesthrough universal joint 14 to drive into the front axle assembly 15. Thefront axle assembly 15 is rigidly secured to the front axle frame 16 bymeans of the bolts 17. The front axle frame 16 is pivotally connectedwith the chassisc 5 by the pivotal assemblies 19 and 20. The steering ofthe drive wheels is accomplished by a suitable steering mechanism.

The vehicle is driven through a transmission and rear drive assembly.Since the drive to the rear wheels is generally conventional, only aportion of the power train for driving the rear wheels is shown.

Referring to FIG. 2, the housing 10 supports the drive train includinggear 21 on shaft 22 driving the pinion 23. Thepinion 23 in turn drivesthe gear 24 in the power train for driving the rear wheels.

Pinion. 23 also drives the gear 25 mounted on the shaft 26. Shaft 26 isembraced by the bearing assemblies 27 and 28 mounted in the housing 10.Gear 25 provides a power take-off for driving the front end drive. Thegear 25 provides a power take-off for the front wheel drive. Thetransfer gear case 9 is fastened to the transmission housing by means ofa plurality of bolts 30. The transfer gear case supports the bearingassemblies 31 and 32 which rotatably support the stub shaft 33. Thebearing retainer 34 carries the seal 35 and is bolted to the transfergear case 9 by the bolts 36.

Clutch collar 37 slidably engages the clutch teeth 38 of gear 39. Theinternal periphery of the clutch collar 37 is splined and slides on thesplined periphery of the clutch sleeve 40. Clutch sleeve 40 in turn hasmating splined portions to engage the splined external periphery ofshaft 33. A shifting fork 41 slides the clutch col,- Iar 37 to engageand disengage the gear 39 with the shaft 33. The fork 41 is connected tothe rod 42 and operated by the clutch link 43. The link 43 in turn isconnected to the clutch control lever l l which is pivotally supportedby the pin 45 on the vehicle chassis 5.

FIG. 3 is a cross section view taken on line III-III of FIG. 2. FIG. 3illustrates a 36 tooth drive gear driving a 37 tooth driven gear 39 inthe transfer gear case 9. The gear case 9 is fastened to the housing 10without any spacers between the mounting surfaces of gear case 9 andhousing 10. The gear centers 46 and 47 are designed to operate with thespacing provided for as shown in FIG. 3.

FIG. 4 illustrates the gear 25 operating on the same gear center 46. Thegear center 48, however, of gears 49 and 50 has been moved downwardlydue to'the use ofa shim 51 between the abutting surfaces of thetransmission housing 10 and transfer gear case 9. Gears 49 and 50 aredesigned to operate with the same gear center relative to gear 25. Gear49 is cut in a manner similar to the gear 39 and operates with gear 25.Gear 25 operates with the same pitch circle 53 when operating with gear39 or gear 49. The gear profile for gear 49 is shown in FIG. 5 by thesolid profile line 52. The pitch circle for gear 25, which is the 36tooth gear, is shown by the line 53 when operating with gears 39 or 49.

Gears 39 and 49 operate with pitch circles 80 and 57 coacting with pitchcircle 53 of gear 25.

Gear 50 operates on the same gear center 48 as does gear 49. Gear 50,however, is a 39 tooth gear. Gear 50 has a tooth profile as indicated bythe profile line 54, as shown in FIG. 5. The gear 50 tooth spacing,being the space between the contact surfaces on the teeth of gear 50with gear 25, is essentially the same as the tooth spacing between thecontact surfaces of gear 49 with gear 25. It is noted, however, that thegear teeth of gear 50 are thinner and extend for a small proportion ofthe circular pitch than on gear 49. When the tooth was formed, the hobcut more deeply to form a deeper root 55 of gear 50 than the root 56 ofgear tooth 49. The modified construction of gear 50 decreases theoperating pitch circle of gear 25 while the operating pitch circle ofgear 50 is greater than the operating pitch circle for gear 49. It isoptional to construct gear 49 in a manner similar to the gear 50construction for operation on the same gear center as gear 39 andwithout the use of shim 51.

Gear 25 operates on the operating pitch circle 59 while operating withgear 50 which operates with a pitch circle 58. Gears 49 and 50, however,operate on the same gear center 48 and a constant gear center ismaintained for gear 25. Accordingly, gear 25 operates on an operatingpitch circle 53 with gear 49 and a pitch circle 59 for gear 50. Thedifference in the operating pitch circles is due to the fact that theteeth of gear 50 have a deeper root 55 and the gear teeth are thinner.

Accordingly, without the shim 51 gear 25 having 36 teeth operates withgear 39 having 37 teeth. With the shim positioned between the housingand gear case, gear 25 operates on the same pitch circle 53 with thegear 49 which has 38 teeth. Although the pitch circle 57 of gear 49 islarger, the gear center 48 has been moved outwardly from the gear center47 of gear 39.

Instead of using another shim between the transfer gear case 9 and thetransmission housing 10 for use with the gear 50, the gear teeth of gear50 are cut narrower to provide a means for operating gear 50 on the samegear center 48 as for gear 49.

The operation of the four wheel drive will be described in the followingparagraphs. V

The engine 4 provides a source of power for driving the vehicle. Thegear 23 drives through gear 24 in the transmission to drive the rearwheels 2. The rear wheels 2 operate at a rolling radius which isessentially the radius between the center of the drive shaft 60 and thecontact point 61 of the tires of the rear wheel 2 with ground. Therolling radius of the rear wheels 2 will determine the speed of theforward movement of the vehicle. Accordingly, the tires 63 on the frontwheel 3 must also have a ground speed at the point of contact 65 of thefront wheel which is substantially the same as the ground speed of thepoint of contact 61 of the rear tire. Accordingly, the rolling radius ofthe front wheel will be a distance from the center line of the axle 66and the contact with the ground 65. It is understood that the rollingradius of either wheel can be changed from normal inflation byoverinflating or underinflating the tires. The rolling radius is alsochanged when a front wheel carries a tire of a thicker tread than aconventional tread. Accordingly, the wear on the tread also affects therolling radius of the wheel.

For operation under normal conditions, the vehicle has adequate tractionon the rear wheels to accommodate the draft load which is applied to thetractor. In this position the clutch collar 37 is positioned as shown,with the clutch collar 37 moved rearwardly so that the teeth 38 of thegear 39 are not engaged. In this position only the rear wheels can drivethe vehicle and the front wheels do not provide any tractive effort.

When it is desired to increase the traction of the vehicle by use of thefour wheel drive, the clutch collar 37 is moved forwardly by actuationof the clutch lever 11 which in turn is adapted to move the clutchcollar 37 forwardly. In this position the teeth 70 of the clutch sleeve40 remain engaged with the clutch collar 37, while the clutch collar 37engages the teeth 38 of gear 39. With engagement of the clutch, thefront wheel drive is then in operation.

The FIGS. 2 and 3 illustrate a normal drive for the front wheel drivemechanism. Gear 25 drives through gear 39. For the purpose ofillustration gear 25 has 36 teeth while the gear 39 has 37 teeth. Gear39 drives the stub shaft 33 which is connected to the propeller shaft13. The propeller shaft 13 drives through the universal joint 14 drivingthe front axle assembly 15 and in turn rotating the front wheels 3.Under .theseconditions, both the front and rear wheels are rotatedproviding traction for the vehicle. With the front wheels and rearwheels driving, the ground speed where a tire meets the terrain aretraveling at substantially the same speed, or preferably the front wheelis traveling at between O-2 percent faster than the ground speed of therear wheels.

When a larger rolling radius of the tires on the front wheel is used onthe tractor, then a slower gear ratio is necessary to match the groundspeed between the front and rear tires. Accordingly, the transfer gearcase 9 is then removed andthe gear 39 is replaced by gear 49 which hasan additional tooth on its periphery. The additional tooth increases thepitch circle of gear 49 with relation to gear 39, and accordingly, whenthe transfer housing is reassembled on the transmissionhousing 10, theshim 51 is placed between the engaging surfaces of the transmissionhousing land transfer gear case 9. This increases the distance betweenthe gear centers 46 and 48to accommodate the increased pitch circle ofgear 49. The gears then operate on pitch circles as indicated bypitchcircle 53 for gear 25, and the pitch circle 57 for gear 49. Thepitch circle 53 of gear remains the same for operation with gear 49. Theangular rotation of the front wheels is decreased slightly, although theground speed remains substantially the same as withoperation, aspreviously described. The provision of a gear 49 having 38 teeth, ascontrasted to gear 39 which has only. 37 teeth, provides a means forcorrelating ground speeds of the different tire sizes.

If an even larger tire for the front wheel is used or a tire with a newtread, or a thicker tread than ordinarily used, the speed of rotation ofthe front wheels must be decreased further to correlate ground speedbetween I the front and rear wheels. Accordingly, the transfer housing 9is removed from the vehicle and the gear 49 is replaced with the gear 50and when the transfer case is again assembled on the transmissionhousing, the shim 51 is inserted between the abutting surfaces of the.transmission housing and transfer gear case 9.

It is noted that the gear 50 has a deeper root on the tooth profilesthangear 49. This in turn increases the effective pitch circle. Theeffective pitch circle 59 of gear 25 is decreased while gear 50 operateson a pitch circle 58. This again decreases the angular velocity. of thefront wheels and correlates the ground speed of the front wheels withthe rear wheels. The manner in which the gear is cut permitsuse of thesame dimension between gear center 25 and 50 as between gear centers 25and 49, although the effective pitch circle changes due to the differentprofile of the teeth on gear 50.

The change-over may be provided in the field, and it is not necessarythat the tractor be returned to the factory to permit the use ofdifferent sizes of tires on the front wheels. The change-over provides ameans of compensating for wear on either the front or rear wheels anddoes not necessitate the replacement of all four tires at one time.

The preferred embodiments of this invention have been illustrated anddescribed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A four wheel drive for a vehicle comprising, a power transmissionadapted for connection to an engine including a drive gear, a pair ofrear wheels defining a predetermined rolling radius, a rear driveassembly for transmitting power from said transmission to said rearwheels, a pair of front wheels defining a predetermined rolling radius,a front wheeldrive mechanism for driving said front wheels, a powertransfer mechanism connected between said front wheel drive mechanismand said transmission including, a driven gear meshing with said drivegear, means selectively changing the operating pitch circle of saiddriven gear relative to said drive gear including, a transfer gear case,means supporting said driven gear in said transfer gear case selectivelyat any one of a number of gear centers, said driven gear selectivelyincluding any one ofa number of gears each including a different numberof gear teeth, and each driven gear defining teeth of any one selectedtooth thickness of a plurality of tooth thicknesses to therebyselectively change the operating pitch circle of said driven gear byselective and alternative changing of the gear center position of saiddriven gear or changing the operating pitch circles of said drive gearand said driven gear by changing of the tooth thickness of said drivengear to provide one of a selected number of gear ratios from saidtransmission through said front wheel drive mechanism to provide apredetermined ground speed of the front wheels relative to the rearwheels to compensate for any change in rolling radius of the frontwheels.

2. A four wheel drive for a vehicle as set forth in claim 1 including atransmission housing supporting said drive gear, said transfer gear casemounted on said housing rotatably supporting said driven gear at a firstgear center with said driven gear defining a predetermined number ofgear teeth thereby providing a first speed ratio for driving the frontwheels.

3. A four wheel drive for a vehicle as set forth in claim 1 including atransmission housing supporting said drive gear, ashim mounted betweensaid transfer gear case and said transmission housing to position saiddriven gear at a second gear center, said driven gear defining saidpredetermined number of gear teeth plus one to thereby provide a secondspeed ratio for driving said front wheels.

4. A four wheel drive for a vehicle as set forth in claim 1 including atransmission housing supporting said drive gear, a shim positionedbetween said transmission housing and said transfer gear case forpositioning said driven gear at a second gear center, said driven gearincluding said predetermined number of gear substantially plus two, saiddriven gear defining gear teeth of less thickness than said drive gearto accommodate operation on said second gear center and for providing athird speed ratio for driving the front wheels.

5. A four wheel drive for a vehicle as set forth in claim l wherein saiddrive gear and said driven gear define a circular pitch substantiallyequal to twice the circular tooth thickness on the operating pitchcircle.

6. A four wheel drive for a vehicle as set forth in claim 1 wherein thedriven gear defines a circular pitch substantially greater than twicethe circular thickness of a gear tooth on the operating pitch circleofsaid driven gear. a l M 7. A four wheel drive for a vehicle as setforth in claim 1 wherein the circular pitch is substantially greaterthan twice the circular tooth thickness thereby shifting the operatingpitch circle away from the gear center of said driven tooth and shiftingthe operating pitch circle toward the gear center of said drive gear todecrease the speed ratio from the drive to the driven gear.

8. A four wheel drive for a vehicle as set forth in claim 1 wherein saiddrive defines a circular pitch equal to substnatially twice the circulartooth thickness, said driven gear defining a circular pitchsubstantially greater than twice the circular tooth thickness to therebyprovide a short addendum tooth for said driven gear.

9. A four wheel drive for a vehicle as set forth in claim 1 wherein saiddriven gear defines a circular pitch substantially greater than twicethe circular tooth thickness, said driven gear defines a short addendumcle of said driven gear.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent, )Io3,763,947 Dated October 9, 1973 Inventor(s) Donald W. Longshore It iscertified that error appears in the above-identified patent and that:said Letters Patent are hereby corrected as shown below:

Column 6, claim 4, line 49, "substantially" should be teeth Column 7,claim 8, line 5, after "drive" insert gear ----7 Column 7,. claim 8,line 6, "substnatially" should be substantially l Signed and sealed this1st day of October 1974.

(SEAL) Attest:

McCOY M.-.GIBSON JR.

Attesting "Officer c. MARSHALL DANN Commissioner of Patents

1. A four wheel drive for a vehicle comprising, a power transmissionadapted for connection to an engine including a drive gear, a pair ofrear wheels defining a predetermined rolling radius, a rear driveassembly for transmitting power from said transmission to said rearwheels, a pair of front wheels defining a predetermined rolling radius,a front wheel drive mechanism for driving said front wheels, a powertransfer mechanism connected between said front wheel drive mechanismand said transmission including, a driven gear meshing with said drivegear, means selectively changing the operating pitch circle of saiddriven gear relative to said drive gear including, a transfer gear case,means supporting said driven gear in said transfer gear case selectivelyat any one of a number of gear centers, said driven gear selectivelyincluding any one of a number of gears each including a different numberof gear teeth, and each driven gear defining teeth of any one selectedtooth thickness of a plurality of tooth thicknesses to therebyselectively change the operating pitch circle of said driven gear byselective and alternative changing of the gear center position of saiddriven gear or changing the operating pitch circles of said drive gearand said driven gear by changing of the tooth thickness of said drivengear to provide one of a selected number of gear ratios from saidtransmission through said front wheel drive mechanism to provide apredetermined ground speed of the front wheels relative to the rearwheels to compensate for any change in rolling radius of the frontwheels.
 2. A four wheel drive for a vehicle as set forth in claim 1including a transmission housing supporting said drive gear, saidtransfer gear case mounted on said housing rotatably supporting saiddriven gear at a first gear center with said driven gear defining apredetermined number of gear teeth thereby providinG a first speed ratiofor driving the front wheels.
 3. A four wheel drive for a vehicle as setforth in claim 1 including a transmission housing supporting said drivegear, a shim mounted between said transfer gear case and saidtransmission housing to position said driven gear at a second gearcenter, said driven gear defining said predetermined number of gearteeth plus one to thereby provide a second speed ratio for driving saidfront wheels.
 4. A four wheel drive for a vehicle as set forth in claim1 including a transmission housing supporting said drive gear, a shimpositioned between said transmission housing and said transfer gear casefor positioning said driven gear at a second gear center, said drivengear including said predetermined number of gear teeth plus two, saiddriven gear defining gear teeth of less thickness than said drive gearto accommodate operation on said second gear center and for providing athird speed ratio for driving the front wheels.
 5. A four wheel drivefor a vehicle as set forth in claim 1 wherein said drive gear and saiddriven gear define a circular pitch substantially equal to twice thecircular tooth thickness on the operating pitch circle.
 6. A four wheeldrive for a vehicle as set forth in claim 1 wherein the driven geardefines a circular pitch substantially greater than twice the circularthickness of a gear tooth on the operating pitch circle of said drivengear.
 7. A four wheel drive for a vehicle as set forth in claim 1wherein the circular pitch is substantially greater than twice thecircular tooth thickness thereby shifting the operating pitch circleaway from the gear center of said driven tooth and shifting theoperating pitch circle toward the gear center of said drive gear todecrease the speed ratio from the drive to the driven gear.
 8. A fourwheel drive for a vehicle as set forth in claim 1 wherein said drivedefines a circular pitch equal to substnatially twice the circular tooththickness, said driven gear defining a circular pitch substantiallygreater than twice the circular tooth thickness to thereby provide ashort addendum tooth for said driven gear.
 9. A four wheel drive for avehicle as set forth in claim 1 wherein said driven gear defines acircular pitch substantially greater than twice the circular tooththickness, said driven gear defines a short addendum tooth profile toeffectively increase the operating pitch circle of said driven gearrelative to said drive gear.
 10. A four wheel drive for a vehicle as setforth in claim 1 wherein said means supporting said driven gear includesa transmission housing, said transfer gear case, a shim positionedbetween said transmission housing and said transfer gear case to definea gear center for said driven gear, said driven gear defines a circularpitch substantially greater than twice the circular tooth thickness tothereby define a short addendum tooth profile for effectively increasingthe operating pitch circle of said driven gear.